Chair back frame



FIG. 1 is a front perspective view of a chair back frame, showing my new design;

FIG. 2 is a front elevational view thereof;

FIG. 3 is a rear elevational view thereof;

FIG. 4 is a left side view thereof;

FIG. 5 is a right side view thereof;

FIG. 6 is a top plan view thereof;

FIG. 7 is a bottom plan view thereof; and,

FIG. 8 is a rear perspective view thereof.

The broken lines showing of the screws in the drawing are for illustrative purposes only and form no part of the claimed design. 

CLAIM The ornamental design for a chair back frame, as shown and described. 